Polishing apparatus

ABSTRACT

A polishing apparatus has a turntable with a polishing cloth attached thereto and a top ring for holding and pressing a workpiece to be polished against the polishing cloth under a certain pressure. The polishing apparatus also has a first dressing unit having a contact-type dresser for dressing the polishing cloth by bringing the contact-type dresser in contact with the polishing cloth, and a second dressing unit having a noncontact-type dresser for dressing the polishing cloth with a fluid jet applied therefrom to the polishing cloth. The contact-type dresser comprises a diamond dresser or an SiC dresser.

[0001] This application is a divisional application of Ser. No.09/622,638, filed Nov. 8, 2000, which is a national stage application ofInternational Application Serial No. PCT/JP99/01543, filed Mar. 26,1999.

TECHNICAL FIELD

[0002] The present invention relates to a polishing apparatus forpolishing a workpiece, such as a semiconductor wafer, to a planarfinish, especially to a device pattern on the surface of thesemiconductor wafer by bringing the surface of the semiconductor waferin contact with a polishing cloth, and particularly to a method ofconditioning the surface of the polishing cloth attached to a turntablein the polishing apparatus.

BACKGROUND ART

[0003] Recent rapid progress in semiconductor device integration demandssmaller and smaller wiring patterns or interconnections and alsonarrower spaces between interconnections which connect active areas. Oneof the processes available for forming such interconnections isphotolithography. Though the photolithographic process can forminterconnections that are at most 0.5 μm wide, it requires that surfaceson which pattern images are to be focused by a stepper be as flat aspossible because the depth of focus of the optical system is relativelysmall.

[0004] It is, therefore, necessary to make the surfaces of semiconductorwafers flat for photolithography. One customary way of flattening thesurfaces of semiconductor wafers is to polish them with a polishingapparatus, and such a process is called Chemical Mechanical Polishing(CMP) in which the semiconductor wafers are chemically and mechanicallypolished while supplying an abrasive liquid comprising abrasive grainsand a chemical solution, such as alkaline solution.

[0005] In the polishing apparatus for polishing the surface of asemiconductor wafer, especially a device pattern on the upper surface ofthe semiconductor wafer, to a planar finish, as a polishing clothattached to a turntable, a nonwoven fabric polishing cloth hasheretofore been employed.

[0006] Higher levels of integration achieved in recent years for ICs andLSI circuits demand smaller steps or surface irregularities on thepolished surface of the semiconductor wafer. In order to meet such ademand, it has been proposed to employ a polishing cloth made of a hardmaterial such as polyurethane foam.

[0007] After the semiconductor wafers are contacted with the polishingcloth and polished by rotating the turntable and the top ring whichholds the semiconductor wafer, the polishing capability of the polishingcloth is gradually deteriorated due to a deposit of abrasive grains andground-off particles of the semiconductor material, and due to changesin the characteristics of the polishing cloth. Therefore, if the samepolishing cloth is used to repeatedly polish semiconductor wafers, thepolishing rate of the polishing apparatus is lowered, and the polishedsemiconductor wafers tend to suffer polishing irregularities. Therefore,it has been customary to condition the polishing cloth according to aprocess called “dressing” for recovering the surface of the polishingcloth before, during or after polishing.

[0008] There are basically two types of dressing processes, one of whichis a contact-type dressing process in which a brush or a diamond dresseris brought into contact with a polishing cloth and rubs the polishingcloth, and the other of which is a noncontact-type dressing process inwhich a fluid jet of water or gas is applied under high pressure to thesurface of the polishing cloth.

[0009] In the conventional polishing apparatus, either a dressing unitcomprising a brush or a diamond dresser, or a dressing unit employing afluid jet has been incorporated therein, depending on the properties ofthe polishing cloth.

[0010] It has been found that when a new polishing cloth is used, itneeds to be dressed by a brush or a diamond dresser for initialconditioning, and while the polishing cloth is being used in a polishingprocess, it needs to be dressed by a fluid jet to remove an aggregate ofabrasive slurry or ground-off particles of the semiconductor materialtherefrom. Unless the polishing cloth is dressed by the fluid jet, thepolished surface of the semiconductor wafer is liable to be scratched,resulting in a poor yield of properly polished semiconductor wafers. Forthe above reasons, these two dressing units are required to be replacedwith each other, when necessary, in the conventional polishingapparatus. Such selective installing and replacing work has been tediousand time-consuming, and is liable to lower the throughput of thesemiconductor wafers.

DISCLOSURE OF INVENTION

[0011] It is therefore an object of the present-invention to provide apolishing apparatus which incorporates both a contact-type dressing unithaving a brush or a diamond dresser and a noncontact-type dressing unitemploying a fluid jet.

[0012] Another object of the present invention is to provide a method ofconditioning the surface of a polishing cloth attached to a turntable insuch a polishing apparatus.

[0013] According to one aspect of the present invention, there isprovided a polishing apparatus comprising a turntable with a polishingcloth attached thereto, a top ring for holding and pressing a workpieceto be polished against the polishing cloth under a certain pressure, afirst dressing unit having a contact-type dresser for dressing thepolishing cloth by bringing the contact-type dresser in contact with thepolishing cloth, and a second dressing unit having a noncontact-typedresser for dressing the polishing cloth with a fluid jet appliedthereto.

[0014] According to another aspect of the present invention, there isprovided a method of conditioning a polishing cloth attached to aturntable for polishing a workpiece. The method comprises dressing thepolishing cloth with a first dressing unit having a contact-type dresseras initial conditioning when the polishing cloth starts to be used, anddressing the polishing cloth with a second dressing unit having anoncontact-type dresser between polishing processes, each for polishingthe workpiece.

[0015] According to still another aspect of the present invention, thereis provided a method of conditioning a polishing cloth attached to aturntable for polishing a workpiece. The method comprises dressing thepolishing cloth with a first dressing unit having a contact-type dresseras initial conditioning when the polishing cloth stalls to be used, anddressing the polishing cloth first with the first dressing unit and thenwith a second dressing unit having a noncontact-type dresser betweenpolishing processes, each for polishing the workpiece.

[0016] The polishing apparatus is equipped with both the contact-typedressing unit, such as a diamond dresser, and the noncontact-typedressing unit, such as a fluid jet dresser. Therefore, it is notnecessary to replace these contact-type and noncontact-type dressingunits with each other on the polishing apparatus, but the contact-typeand noncontact-type dressing units may be combined to carry out adesired pattern of dressing processes to dress or condition thepolishing cloth.

[0017] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwhen taken in conjunction with the accompanying drawings whichillustrate a preferred embodiment of the present invention by way ofexample.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a plan view of a polishing apparatus according to thepresent invention;

[0019]FIG. 2 is an elevational view, partly in cross section, takenalong line II-II of FIG. 1;

[0020]FIG. 3A is a bottom view of a diamond dresser in a first dressingunit incorporated in the polishing apparatus;

[0021]FIG. 3B is a cross-sectional view taken along line a-a of FIG. 3A;

[0022]FIG. 3C is an enlarged view of an encircled area b in FIG. 3B;

[0023]FIG. 4 is an elevational view of a second dressing unit comprisinga fluid jet dresser incorporated in the polishing apparatus; and

[0024]FIGS. 5A and 5B are timing charts of different patterns ofpolishing and dressing sequences carried out by the polishing apparatus.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Next, a polishing apparatus according to the present inventionwill be described with reference to the drawings.

[0026] As shown in FIGS. 1 and 2, a polishing apparatus according to thepresent invention comprises a turntable 20 and a top ring unit 4 havinga top ring 3 for holding a semiconductor wafer 2 to be polished andpressing the semiconductor wafer 2 against the turntable 20. Theturntable 20 is coupled to a motor 21 by a vertical shaft, and rotatableabout the vertical shaft. A polishing cloth 5, such as IC-1000manufactured by Rodel, Inc., is attached to the tipper surface of theturntable 20.

[0027] A pusher 40 is positioned on one side of the turntable 20adjacent to the top ring unit 4. The top ring unit 4 is angularlymovable in a horizontal plane to move the top ring 3 between a transferposition above the pusher 40 where the semiconductor wafer 2 istransferred to and from the pusher 40, a polishing position over theturntable 20, and a standby position off the turntable 20. The top ring3 is coupled to a motor and a lifting/lowering cylinder (not shown). Thetop ring 3 is vertically movable by the lifting/lowering cylinder and isalso rotatable about its own axis by the motor as indicated by thearrows (see FIG. 2). When the top ring 3 is lowered toward the turntable20, the top ring 3 presses the semiconductor wafer 2 against thepolishing cloth 5 on the turntable 20 under a predetermined pressure.The top ring 3 has a holding mechanism (not shown) for holding thesemiconductor wafer 2 by its lower surface under a vacuum. A guide ring6 is mounted on a lower outer circumferential surface of the top ring 3,whereby the semiconductor wafer 2 is retained against removal from thelower surface of the top ring 3. An abrasive liquid containing abrasivegrains is supplied to the polishing cloth 5 on the turntable 20 by anabrasive liquid supply nozzle (not shown) which is positioned above theturntable 20.

[0028] The polishing apparatus also has a first dressing unit 11 havinga contact-type dresser 10, and a second dressing unit 16 having anoncontact-type dresser comprising a plurality of water jet nozzles 15.The first dressing unit 11, which is positioned diametrically oppositeto the top ring unit 4 and the pusher 40 across the turntable 20, isangularly movable in a horizontal plane between a dressing position overthe turntable 20 and a standby position off the turntable 20. As shownin FIG. 2, the dresser 10 is connected to a motor 17 and alifting/lowering cylinder 18. The dresser 10 is vertically movable bythe lifting/lowering cylinder 18 and is also rotatable about its ownaxis by the motor 17 as indicated by the arrows (see FIG. 2).

[0029]FIGS. 3A, 3B, and 3C show in detail the dresser 10 of the firstdressing unit 11. As shown in FIGS. 3A, 3B and 3C, the dresser 10comprises a circular disk-shaped dresser body 12 having an annularprojection 12 a extending along a lower circumferential edge thereof andhaving a predetermined radial width. The dresser 10 will also bereferred to as a diamond dresser 10. The dresser 10 has anelectrodeposited diamond ring 13 which comprises fine grains of diamondelectrodeposited on the lower surface of the annular projection 12 a.Specifically, the electrodeposited diamond ring 13 is produced byattaching fine grains of diamond to the lower surface of the annularprojection 12 a and then plating the lower surface of the annularprojection 12 a with nickel for thereby fixing the fine grains ofdiamond with a plated nickel layer.

[0030] In operation, while the turntable 20 and the dresser 10 arerotated relative to each other, and a dressing liquid such as pure wateror an abrasive liquid is supplied from a nozzle (not shown) to asubstantially central region of the polishing cloth 5, the lower surfaceof the electrodeposited diamond ring 13 is held against the uppersurface of the polishing cloth 5 to scrape off a thin layer of thepolishing cloth 5, thereby dressing the polishing cloth 5.

[0031] The dresser body 12 has a diameter of 250 mm, and theelectrodeposited diamond ring 13 oil the lower end of the annularprojection 12 a has a radial width of 6 mm. As shown in FIG. 3A, theelectrodeposited diamond ring 13 comprises a plurality of equal arcuatesectors (eight in the illustrated embodiment). The diameter of thedresser body 12 is greater than the diameter of the semiconductor wafer2 to be polished. When the semiconductor wafer 2 is polished, therefore,the dressed surface of the polishing cloth 5 provides an extra marginwith respect to the polished surface of the semiconductor wafer 2 inboth radial inward and outward directions of the turntable 20. Thedresser 10 may be replaced with an SiC dresser having a ring of sectorsmade of silicon carbide. The SiC dresser has a structure identical tothe structure shown in FIGS. 3A-3C, and has on the surfaces of itssectors a number of pyramidal projections each having a height of aboutseveral tens of μm.

[0032]FIG. 4 shows structural details of the second dressing unit 16. Asshown in FIG. 4, the second dressing unit 16 comprises an array of sixwater jet nozzles 15 positioned over the polishing cloth 5 and equallyspaced radially of the polishing cloth 5. The water jet nozzles 15 arefixedly mounted oil a water jet nozzle arm 22 having a liquid passage 22a defined therein. Pure water supplied from a pure water source (notshown) is pressurized by a pump 26 and supplied through a tube 23 andthe liquid passage 22 a to the water jet nozzles 15, from which purewater jets are ejected downward toward the polishing cloth 5.

[0033] The water jet nozzles 15 are positioned and oriented to apply thepure water jets ejected therefrom to an area of the polishing cloth 5which is used to polish the semiconductor wafer 2, i.e., an area of thepolishing cloth 5 against which the semiconductor wafer 2 is pressed soas to be polished. The water jet nozzle arm 22 is fixed in a positionabove the polishing cloth 5 by a vertical support 22 b. However, thewater jet nozzle arm 22 may be angularly movable in a horizontal planeabout the vertical axis of the vertical support 22 b for fine positionaladjustment thereof and/or for a standby position located radiallyoutward of the polishing cloth 5 for maintenance thereof.

[0034] The pure water flowing through the water jet nozzle arm 22 iskept at a predetermined pressure by a controller (not shown) for thepump 26. The water jet nozzles 15 are identical in structure to eachother, so that they eject respective water jets under substantially thesame pressure at substantially the same rate. The pressure of theejected water jets can be maintained in the range of 5 to 30 kg/cm² bycontrolling the pump 26.

[0035] When the polishing cloth 5 is dressed by the second dressing unit16, the turntable 20 and hence, the polishing cloth 5, are rotated tothereby apply the water jets ejected from the water jet nozzles 15 tothe entire surface of the polishing cloth 5. Since the polishing cloth 5is held in contact with the water jets for a period of time which isprogressively shorter in the radially outward direction, the dressingeffect on the polishing cloth 5 which is caused by the water jets mayvary depending on the radial position on the polishing cloth 5.Therefore, in order to uniformize the dressing effect on the polishingcloth 5, the number of water jet nozzles 15 may be increased in theradially outward direction, or the water jet nozzles 15 may eject waterjets at a progressively higher speed in the radially outward direction.Alternatively, the distance between the nozzle outlet and the polishingcloth 5 may vary from nozzle to nozzle. Further, the pressure and thespeed at which the water jet is ejected may be made variable at each ofthe water jet nozzles 15.

[0036] Polishing and dressing processes which are carried out by thepolishing apparatus shown in FIGS. 1 through 4 will be described withreference to FIGS. 5A and 5B. FIGS. 5A and 5B are timing charts ofdifferent patterns of polishing and dressing sequences carried out bythe polishing apparatus.

[0037] According to the pattern of polishing and dressing sequencesshown in FIG. 5A, when the polishing cloth 5 starts to be used, it isfirst dressed by the diamond dresser 10 for initial conditioning.Thereafter, a semiconductor wafer 2 is polished using the dressedpolishing cloth 5. Between polishing processes, the polishing cloth 5 isdressed by the water jet nozzles 15 with water jets ejected therefrom.

[0038] According to the pattern of polishing and dressing sequencesshown in FIG. 5B, when the polishing cloth 5 starts to be used (i.e.,before it is used for polishing), it is first dressed by the diamonddresser 10 for initial conditioning. Thereafter, a semiconductor wafer 2is polished using the dressed polishing cloth 5. Between polishingprocesses, the polishing cloth 5 is dressed in two steps, i.e., first bythe diamond dresser 10 and then by the water jet nozzles 15 with waterjets ejected therefrom.

[0039] As shown in FIGS. 5A and 5B, according to the polishing apparatusof the present invention, after initial conditioning of the polishingcloth 5 by the diamond dresser 10, a polishing process of thesemiconductor wafer is carried out, and after completing the polishingprocess, dressing of the polishing cloth 5 by the wafer jet is carriedout. Thereafter, polishing process is candied out again. Further,between polishing processes, dressing of the polishing cloth 5 by thediamond dresser and the water jet may be combined.

[0040] In the illustrated embodiment, the contact-type dresser of thefirst dressing unit 11 comprises the diamond dresser 10. However, thediamond dresser may be replaced with a brush dresser. Furthermore, purewater is used as the dressing liquid in the first dressing unit 11 andalso as the water jets in the second dressing unit 16. However,chemicals such as alkaline liquid or surface-active agent may be used inthe first and second dressing units 11 and 16 for performing a chemicaldressing action in addition to a mechanical dressing action.

[0041] Inasmuch as the polishing apparatus according to the presentinvention is equipped with both the first dressing unit 11 having thecontact-type dresser comprising the diamond dresser 10 and the seconddressing unit 16 having the noncontact-type dresser comprising the waterjet nozzles 15, it is not necessary to replace two dressing units as inthe conventional polishing apparatus, and the two dressing units 11, 16may be combined to carry out a desired pattern of dressing processes. Ifthe polishing apparatus is applied to the fabrication of semiconductordevices, then semiconductor devices can be manufactured in a high yieldwith high productivity.

[0042] Although a certain preferred embodiment of the present inventionhas been shown and described in detail, it should be understood thatvarious changes and modifications may be made therein without departingfrom the scope of the appended claims.

INDUSTRIAL APPLICABILITY

[0043] The present invention relates to a polishing apparatus forpolishing a workpiece such as a semiconductor wafer to a planar finish,and is preferably utilized in manufacturing semiconductor devices.

What is claimed is:
 1. A method of polishing a workpiece in a polishingapparatus, comprising: conditioning a polishing surface by acontact-type dresser for initial conditioning before starting using saidpolishing surface; polishing a workpiece by bringing said workpiece intocontact with said polishing surface after said conditioning; anddressing said polishing surface after said polishing by anoncontact-type dresser for removing ground-off particles of saidworkpiece.
 2. A method according to claim 1, wherein saidnoncontact-type dresser and said contact-type dresser are provided insaid polishing apparatus.
 3. A method according to claim 1, wherein saidnoncontact-type dresser comprises a plurality of fluid jet nozzles forejecting fluid jets.
 4. A method according to claim 3, wherein thepressure of each of said nozzles is variable.
 5. A method according toclaim 1, wherein said contact-type dresser comprises a diamond dresser.6. A method according to claim 1, wherein said polishing surface isdressed by said contact-type dresser before said dressing of saidpolishing surface by said noncontact-type dresser.
 7. A method accordingto claim 1, wherein said noncontact-type dresser is angularly movable toa standby position located outwardly of said polishing surface.
 8. Amethod according to claim 7, wherein said contact-type dresser isangularly movable to a standby position located outwardly of saidpolishing surface.
 9. A method of polishing workpieces in a polishingapparatus, comprising: attaching a member having a polishing surface toa table; conditioning said polishing surface by a contact-type dresserfor initial conditioning before starting using said polishing surface;polishing workpieces repeatedly by bringing each of said workpieces intocontact with said polishing surface after said conditioning whilesupplying an abrasive liquid in said polishing; and dressing saidpolishing surface between said polishing of said workpieces by anoncontact-type dresser for removing ground-off particles of saidworkpieces.
 10. A method according to claim 9, further comprisingholding said each of said workpieces by a vacuum.
 11. A method accordingto claim 9, wherein said noncontact-type dresser comprises a pluralityof fluid jet nozzles for ejecting fluid jets.
 12. A method according toclaim 1 wherein the pressure of each of said nozzles is variable.
 13. Amethod according to claim 9, wherein said contact-type dresser comprisesa diamond dresser.
 14. A method according to claim 9, wherein saidpolishing surface is dressed by said contact-type dresser before saiddressing of said polishing surface by said noncontact-type dresser. 15.A method of polishing a workpiece in a polishing apparatus, comprising:attaching a member having a polishing surface to a table; conditioningsaid polishing surface for initial conditioning before starting usingsaid polishing surface; polishing a workpiece by bringing said workpieceinto contact with said polishing surface after said conditioning; anddressing said polishing surface after said polishing for removingground-off particles of said workpiece.